Mapping
GoAn important data type provided by programming is mapping，Uniquely map a key to a value。 An object to be used to retrieve the value later. Given keys and values，Can be in oneMapThe value of the object store。 After the value is stored, you can use its key to retrieve it.
Define the map
A map must be created using the make function.
/* declare a variable, by default map will be nil*/
var map_variable map[key_data_type]value_data_type
/* define the map as nil map can not be assigned any value*/
map_variable = make(map[key_data_type]value_data_type)
example
The following examples illustrate the use of creation and mapping.
package main
import "fmt"
func main {
var coutryCapitalMap map[string]string
/* create a map*/
coutryCapitalMap = make(map[string]string)
/* insert key-value pairs in the map*/
countryCapitalMap["France"] = "Paris"
countryCapitalMap["Italy"] = "Rome"
countryCapitalMap["Japan"] = "Tokyo"
countryCapitalMap["India"] = "New Delhi"
/* print map using keys*/
for country := range countryCapitalMap {
("Capital of",country,"is",countryCapitalMap[country])
}
/* test if entry is present in the map or not*/
captial, ok := countryCapitalMap["United States"]
/* if ok is true, entry is present otherwise entry is absent*/
if(ok){
("Capital of United States is", capital)
}else {
("Capital of United States is not present")
}
}
Let's compile and run the above program, which will produce the following results:
Capital of India is New Delhi Capital of France is Paris Capital of Italy is Rome Capital of Japan is Tokyo Capital of United States is not present
delete() function
The delete() function is used to delete an item from the map. The map and the corresponding keys will be deleted. Here is an example:
package main
import "fmt"
func main {
/* create a map*/
coutryCapitalMap := map[string] string {"France":"Paris","Italy":"Rome","Japan":"Tokyo","India":"New Delhi"}
("Original map")
/* print map */
for country := range countryCapitalMap {
("Capital of",country,"is",countryCapitalMap[country])
}
/* delete an entry */
delete(countryCapitalMap,"France");
("Entry for France is deleted")
("Updated map")
/* print map */
for country := range countryCapitalMap {
("Capital of",country,"is",countryCapitalMap[country])
}
}
Let's compile and run the above program, which will produce the following results:
Original Map Capital of France is Paris Capital of Italy is Rome Capital of Japan is Tokyo Capital of India is New Delhi Entry for France is deleted Updated Map Capital of India is New Delhi Capital of Italy is Rome Capital of Japan is Tokyo
method
The Go programming language supports methods of special types of function calls. In the syntax of method declaration, the "receiver" exists to represent functions in the container. This receiver can be used to call the function "." operator. Here is an example:
grammar
func (variable_name variable_data_type) function_name() [return_type]{
/* function body*/
}
package main
import (
"fmt"
"math"
)
/* define a circle */
type Circle strut {
x,y,radius float64
}
/* define a method for circle */
func(circle Circle) area() float64 {
return * *
}
func main(){
circle := Circle(x:0, y:0, radius:5)
("Circle area: %f", ())
}
When the above code is compiled and executed, it produces the following results:
Circle area: 78.539816